The core of a conventional MEMS condenser microphone is a variable capacitor, which commonly is formed from a static, unmovable substrate/backplate and an opposed movable diaphragm. In operation, audio signals strike the movable diaphragm, causing it to vibrate, thus varying the distance between the diaphragm and the backplate. This varying distance changes the variable capacitance, consequently producing an electrical signal that is directly related to the incident audio signal.
The backplate often has an unintended curvature caused from intrinsic stresses of the fabrication, assembly, and packaging processes. Undesirably, this curvature can create significant sensitivity variations in a MEMS microphone.